Products of diepoxide polyaddition with monofunctional initiators, which contain pendant epoxy groups in the backbone of the polymer

ABSTRACT

The invention relates to water-dilutable binders for cationic electrocoating finishes. For the preparation of the binders, a di-epoxide compound, together with at least one mono-epoxide compound if desired, is converted by a polyaddition, carried out at 100° to 195° C. and initiated by a monofunctionally reacting initiator carrying either an alcoholic OH group, a phenolic OH group or an SH group, to form an epoxy resin which then subsequently is modified with 
     (A) primary and/or secondary amines or their salts and/or the salt of a tertiary amine, a sulfide/acid mixture or a phosphine/acid mixture and with, if desired, 
     (B) a polyfunctional alcohol, a polycarboxylic acid, a polysulfide or a polyphenol.

The present invention relates to water-dilutable binders for cationicelectrocoating finishes, based on modified epoxy resins containingammonium, sulfonium and/or phosphonium groups.

Cationic electrocoating is a coating process frequently used especiallyfor priming, in which synthetic resins carrying water-dilutable cationicgroups are deposited by direct current on electrically conductingobjects.

The use of modified epoxy resins as binders for cationic electrocoatingfinishes is known (U.S. Pat. No. 4,104,147; U.S. Pat. No. 4,260,720).

Modified epoxy resins that have been hitherto available for use incationic electrocoating finishes are only poorly compatible withaliphatic hydrocarbons, are in need of improvement in respect of theirflexibility and give rise to coatings that cannot be overcoated withoutproblems and whose thickness should be further increased.

An object of the present invention was to develop novel modified epoxyresins that would be free from the disadvantages outlined above.

The object according to the invention was achieved by the development ofbinders which were prepared by

(a) a polyaddition of a di-epoxide compound and/or a mixture ofdi-epoxide compounds, together with at least one monoepoxide compound ifdesired, carried out at 100° to 195° C., if desired in the presence of acatalyst, initiated by a monofunctionally reacting initiator carryingeither an alcoholic OH group, a phenolic OH group or SH group, to forman epoxy resin in which the di-epoxide compound and the initiator areincorporated in a molar ratio of >2:1 to 10:1, and by a subsequent

(b) modification of the epoxy resin obtained from (a) with

(A) a primary and/or secondary amine or their salts and/or the salt of atertiary amine, a sulfide/acid mixture or phosphine/acid mixture or amixture of these compounds, and, if desired, with

(B) a polyhydric alcohol, a polycarboxylic acid, a polyamine, apolysulfide, a polyphenol or a mixture of these compounds and, ifdesired,

(c) by protonization with a water-soluble acid.

It was found that the modified epoxy resins prepared by the polyadditiondescribed above and subsequent modification with the component (A) aredistinguished by good compatibility with aliphatic hydrocarbons and highelasticity. Their use as binders in cationic electrocoating finishesleads to the deposition of thick coatings which can be readilyovercoated.

Additional reaction with the component B can lead to a further increasein elasticity of the modified epoxy resins as well as to an additionalincrease in the thickness of the deposited coatings.

In addition, the novel modified epoxy resins have the advantage of beingpreparable from readily accessible raw materials.

All compounds which contain two reactive epoxide groups and have anepoxide equivalent weight below 500, can be used as the di-epoxidecompounds.

Diglycidyl ethers of polyphenols, prepared from polyphenols andepihalohydrins, are particularly preferred epoxide compounds. Examplesof polyphenols which can be used are:

Very particularly preferred: bisphenol A and bisphenol F

particularly preferred: 1,1-bis-(4-hydroxyphenyl)n-heptane. Othersuitable compounds are 4,4'-dihydroxybenzophenone,bis-(4-hydroxyphenyl)-1,1-ethane, bis-(4-hydroxyphenyl)-1,1-isobutane,bis-(4-hydroxy-tert-butylphenyl)-2,2-propane,bis-(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthalene and phenolicnovolak resins.

Preferred epoxide compounds are also diglycidyl ethers of polyhydricalcohols such as ethylene glycol, diethylene glycol, triethylene glycol,1,2-propylene glycol, 1,4-propylene glycol, 1,5-pentanediol,1,2,6-hexanetriol, glycerol and bis-(4-hydroxycyclohexyl)-2,2-propane.

Diglycidyl esters of polycarboxylic acids, for example oxalic acid,succinic acid, glutaric acid, terephthalic acid,2,6-naphthalenedicarboxylic acid, dimerized linolenic acid, etc., can bealso used. Typical examples are glycidyl adipate and glycidyl phthalate.

Other suitable compounds are hydantoin epoxides, epoxidizedpolybutadiene and di-epoxide compounds, obtainable by epoxidization ofan olefinically unsaturated alicyclic compound.

Besides the di-epoxide compounds, mono-epoxide compounds can also beused as additional starting materials for the polyaddition.

All compounds which contain only one epoxide group, are in principlesuitable.

Examples of mono-epoxide compounds which are preferably used are phenylglycidyl ether and the glycidyl esters of versatic and (meth)acrylicacid.

All compounds which react monofunctionally under the reaction conditionsprevailing at the start of the polyaddition and contain an alcoholic OHgroup, a phenolic OH group or an SH group can be used as initiators.

The initiators used can be compounds of the general formula

    ______________________________________                                        R.sup.1OH                                                                     in which R.sup.1 can have the following meaning                               R.sup.1 =                                                                           alkyl                                                                         (preferably of 1 to 20 carbon atoms, particularly                             preferably methyl, ethyl, (iso)propyl, (iso)-                                 butyl, (iso)amyl, 2-ethylbutyl, 2-ethylhexyl,                                 isononyl, isodecyl, isotridecyl, isohexadecyl,                                isooctadecyl, neopentyl, 3,7-dimethyl-3-octyl,                                3-cyclohexylpropyl, 2,4-dimethyl-3-pentyl).                             =     alkenyl                                                                       (particularly preferably 1-buten-3-yl,                                        2-methylbut-3-en-2-yl, 3-methylpent-1-en-3-yl                           =     R.sup.2XR.sup.3,                                                              in which                                                                R.sup.2 = alkyl (of 1 to 6 carbon atoms, preferably methyl,                             ethyl, butyl or hexyl) or phenyl                                    R.sup.3 = CH.sub.2 CH.sub.2(OCH.sub.2CH.sub.2).sub.n with n = 0 to 10,                  especially 0, 1 and 2, propyl or butyl                              X =       O or S                                                              =     cycloalkyl,                                                                   particularly preferably cyclohexyl, preferably                                4-tert-butylcyclohexyl                                                  =     aryl,                                                                         particularly preferably                                                        ##STR1##                                                               R.sup.4 = H, alkyl (preferably of 1 to 20 carbon atoms,                                 particularly preferably tert-butyl,                                           nonyl and dodecyl)                                                  R.sup.4 =                                                                           R.sup.5O                                                                      (preferably in the para-position to the phenolic                              OH group) in which                                                      R.sup.5 = alkyl (preferably of 1 to 10 carbon atoms,                                    particularly preferably methyl)                                     R.sup.1 =                                                                           aralkyl,                                                                      preferably benzyl, 4-methylbenzyl, phenylethyl,                               2-phenylprop-1-yl                                                             or a compound of the general formula R.sup.6SH,                               in which R.sup.6 can have the following meaning                         R.sup.6 =                                                                           alkyl                                                                         (preferably of 1 to 20 carbon atoms, particularly                             preferably n-butyl and dodecyl)                                         =     R.sup.7OOC(CH.sub.2).sub.n in which n = 1 or 2 and                      R.sup.7 = alkyl radical of 1 to 8 carbon atoms (preferably                              butyl or 2-ethylhexyl)                                              =     cycloalkyl, particularly cyclohexyl                                     =     aryl, particularly preferably phenyl                                    =     aralkyl, particularly preferably benzyl                                 ______________________________________                                    

or a mixture of these compounds.

In addition, monofunctional prepolymers, for example reaction productsof one of the monofunctional compounds mentioned above with lactones,for example, δ-caprolactone, can be also used as initiators.

Primary or secondary amines and their salts, salts of tertiary amines,sulfide/acid mixtures of phosphine/acid mixtures or a mixture of thesecompounds can be used as component A, the secondary amines beingespecially preferred components A.

The amine should preferably be a water-soluble compound. Examples ofsuch amines are mono- and dialkylamines, such as methylamine,ethylamine, propylamine, butylamine, dimethylamine, diethylamine,dipropylamine, methylbutylamine and the like. Alkanolamines, for examplemethylethanolamine, diethanolamine and the like, are likewise suitable.Dialkylaminoalkylamines, for example dimethylaminoethylamine,diethylaminopropylamine, dimethylaminopropylamine and the like are alsosuitable.

In the majority of cases, low molecular weight amines are used, but itis also possible to use relatively high molecular weight monoamines.

Polyamines possessing primary and secondary amino groups can react withthe epoxide groups in the form of their ketimines. The ketimines areprepared from the polyamines in a known manner.

The amines can also contain other groups, but these should not interferewith the reaction of the amine with the epoxide group and, equally,should not lead to gelling of the reaction mixture.

The charges required for dilutability with water and electrodepositioncan be produced by protonation with water-soluble acids (for exampleboric acid, formic acid, lactic acid, propionic acid, butyric acid,hydrochloric acid, phosphoric acid, sulfuric acid, carbon dioxide and,preferably, acetic acid) or by reacting the oxirane groups with salts ofan amine or a sulfide/acid mixture or phosphine/acid mixture.

The salt of a tertiary amine can be used as the salt of an amine.

The amine part of the amine acid salt is an amine which can beunsubstituted or substituted, as is the case with hydroxylamine, andthese substituents should not interfere with the reaction of the amineacid salt with the polyepoxide and not cause gelling of the reactionmixture. Preferred amines are tertiary amines, such asdimethylethanolamine, triethylamine, trimethylamine, triisopropylamineand the like. Examples of other suitable amines are given in U.S. Pat.No. 3,839,525 in column 5, line 3 to column 7, line 42.

The amine/acid salt mixture is obtained by reaction of the amine withthe acid in a known manner. Amine/acid mixtures can be also used,although they react as a rule with the formation of the acid salt.

A reaction of the oxirane groups with a sulfide in the presence of anacid gives rise to resins containing sulfonium groups.

Any sulfides which react with epoxide groups and do not contain groupsthat would interfere with the reaction can be used as sulfides. Thesulfide can be an aliphatic, mixed aliphatic-aromatic, aralkyl or cyclicsulfide. Example of such sulfides are dialkyl sulfides, such as diethylsulfide, dipropyl sulfide, dibutyl sulfide, dihexyl sulfide, or alkylphenyl sulfides, such as diphenyl sulfide, ethyl phenyl sulfide, oralicyclic sulfides, such as tetramethylene sulfide and pentamethylenesulfide, or hydroxyalkyl sulfides, such as thiodiethanol,thiodipropanol, thiodibutanol and the like.

Any acid which forms a tertiary sulfonium salt can be used as acid. Anorganic carboxylic acid is, however, preferred as the acid. Examples ofsuitable acids are boric acid, formic acid, lactic acid, acetic acid,propionic acid, butyric acid, hydrochloric acid, phosphoric acid andsulfuric acid. The acid has preferably a dissociation constant greaterthan about 1×10⁻⁵.

The sulfide:acid ratio is not particularly critical. Since oneequivalent of an acid is used for the formation of one mole of asulfonium group, at least one equivalent of an acid is preferably usedfor each desired mole of the conversion of sulfide to sulfonium.

A reaction of the oxirane groups with a phosphine in the presence of anacid gives rise to resins containing phosphonium groups.

Any phosphine that contains no interfering groups can be used asphosphine. Examples of such phosphines are aliphatic, aromatic oralicyclic phosphines, the following phosphines being specific examples:

Low trialkylphosphines, such as trimethylphosphine, triethylphosphine,tripropylphosphine, tributylphosphine, or mixed lowalkylphenylphosphines, such as phenyldimethylphosphine,phenyldiethylphosphine, phenyldipropylphosphine,diphenylmethylphosphine, diphenylethylphosphine,diphenylpropylphosphine, triphenylphosphine, or alicyclic phosphines,such as tetramethylene-ethylphosphine, and the like.

Any acid that forms a quaternary phosphonium salt can be used as theacid. An organic carboxylic acid is, however, preferred as the acid.Examples of suitable acids are boric acid, lactic acid, formic acid,acetic acid, propionic acid, butyric acid, hydrochloric acid, phosphoricacid and sulfuric acid.

The acid should preferably have a dissociation constant greater thanabout 10⁻⁵.

The phosphine:acid ratio is not especially critical. Since oneequivalent of an acid is required for the formation of one mole of aphosphonium group, at least about one equivalent of an acid ispreferably used for each mole of the desired conversion of phosphone tophosphonium.

The polyfunctional alcohols, polycarboxylic acids, polyamines orpolysulfides suitable for use as component B have a molecular weight offrom 300 to 3,500, preferably from 350 to 1,000.

The polyols suitable for the invention include diols, triols and higherpolymeric polyols such as polyester polyols and polyether polyols.

The polyalkylene ether polyols suitable for component B correspond tothe general formula:

    H--O--(CHR).sub.n ].sub.m OH

in which R=hydrogen or a low alkyl radical, if desired with varioussubstituents, n=2 to 6 with m=3 to 50 or even higher. Examples arepoly(oxytetramethylene) glycols and poly(oxyethylene) glycols.

The preferred polyalkylene ether polyols are poly(oxytetramethylene)glycols with a molecular weight in the range from 350 to 1,000.

Polyester polyols can likewise be used as the polymeric polyolcomponents (component B) in the invention. The polyester polyols can beprepared by polyesterification of organic polycarboxylic acids or theiranhydrides with organic polyols containing primary hydroxyl groups. Thepolycarboxylic acids and the polyols are usually aliphatic or aromaticdicarboxylic acids and diols.

The diols used for the preparation of the polyesters include alkyleneglycols, such as ethylene glycol, butylene glycol, neopentyl glycol, andother glycols, such as cyclohexanedimethanol.

The acid component of the polyester consists primarily of low molecularweight carboxylic acids or their anhydrides with 2 to 18 carbon atoms inthe molecule. Examples of suitable acids are phthalic acid, isophthalicacid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalicacid, adipic acid, azelaic acid, sebacic acid, maleic acid and glutaricacid. The corresponding anhydrides, in so far as these exist, can beused instead of these acids.

In addition, polyester polyols derived from lactones can be also used ascomponent B in the invention. These products are obtained by thereaction of a ε-caprolactone with a polyol. Such products as describedare described in U.S. Pat. No. 3,169,945.

The polylactone polyols, obtained by this reaction, are distinguished bythe presence of a terminal hydroxyl group and by recurring polyestermoieties derived from the lactone. These recurring molecular moietiescan correspond to the formula ##STR2## in which n is at least 4,preferably 4 to 6, and the substituent is hydrogen or an alkyl, acycloalkyl or an alkoxy radical.

Long-chain dicarboxylic acids are used in a further advantageousembodiment of the invention. Examples of these are dimeric fatty acids,such as, for example, dimeric linoleic acid.

Polyamines which are suitable for rendering the coatings elastic can beproduced by, for example, reacting primary diamines with monoepoxides.The secondary, substituted diamines formed modify the epoxy resinsaccording to the invention in a suitable manner.

Primary-tertiary diamines or alkanolamines, such as aminoethanol oraminopropanol, can also be used as component B.

Reaction products of organic dihalides with sodium polysulfide aresuitable polyfunctional SH compounds (component B). Other SH compoundsare, for example, the reaction products of hydroxyl-containing linearpolyesters, polyethers or polyurethanes with mercaptocarboxylic acids,such as mercaptoacetic acid, 2-mercaptopropionic acid,3-mercaptopropionic acid, mercaptobutyric acid and the like.

Polyphenols which are suitable as component B correspond to the generalformula (I) explained above. ##STR3## This component B can beadvantageously prepared, for example, in the following manner. One moleof a high-molecular diol, for example a polyester diol, apolycaprolactone diol, a polyether diol, a polycarbonate diol or thelike, is esterified with two moles of a hydroxyphenylcarboxylic acid oris reacted with two moles of a hydroxyphenylcarboxylic acid ester.Suitable hydroxycarboxylic acids are p-hydroxybenzoic acid,p-hydroxyphenylacetic acid and 3-(4-hydroxyphenyl)propionic acid ortheir esters. If the introduction of the hydroxyphenyl group is carriedout by transesterification, a basic transesterification can also becarried out using the alkali metal phenolates of the correspondinghydroxyphenylcarboxylic acid esters. To obtain the desired polyphenol,it is necessary to work up the product at the end of the reaction underacid conditions.

N-(4-hydroxyphenyl)glycine, for example, can also be used for directesterification. In a further variant, any acid polyesters can be reactedwith p-hydroxyaniline to give the desired polyphenols.

In another advantageous embodiment, polyether diamines or similarpolyamines are reacted, with, for example,4-hydroxy-3-methoxybenzaldehyde to form the polyphenols.

The binders prepared according to the invention can be crosslinked bymethods known per se by the addition of crosslinking agents or convertedto self-crosslinking systems by chemical modification. Aself-crosslinking system can be obtained, for example, by reacting thebinder with a partially blocked polyisocyanate which has on average onefree isocyanate group per molecule and whose blocked isocyanate groupsonly become unblocked at elevated temperatures.

Virtually all at least bifunctional compounds which react with oxiranegroups, for example polyalcohols, polyphenols, polycarboxylic acids,polycarboxylic acid anhydrides and acid amides, polyamines,polyisocyanates, phenoplasts, etc., are suitable crosslinking agents.

The crosslinking agents are usually used in amounts from 5 to 60,preferably from 20 to 40, % by weight, based on the binder.

Methods that are frequently used for the crosslinking of binders arepublished, for example, in the following patent documents: British Pat.No. 1,303,480, European Patent Application No. 12,463 U.S. Pat. No.4,252,703 and British Pat. No. 1,557,516.

Examples of suitable aminoplast crosslinking agents are the hexamethylether of hexamethylolmelamine, the triethyl trimethyl ether ofhexamethylolmelamine, the hexabutyl ether of hexamethylolmelamine andthe hexamethyl ether of hexamethylolmelamine, and polymeric butylatedmelamine-formaldehyde resins. Alkylated urea-formaldehyde resins arelikewise suitable.

Blocked polyisocyanates are preferably used as crosslinking agents. Inthe invention, any polyisocyanate can be used whose isocyanate groupsare reacted with a compound in such a manner that the blockedpolyisocyanate formed is non-reactive toward hydroxyl groups at roomtemperature, but reacts at elevated temperatures, usually in the regionfrom about 90° to about 300° C. To prepare the blocked polyisocyanates,any organic polyisocyanates suitable for the crosslinking can be used.The isocyanates which contain from about 3 to about 36, in particularfrom about 8 to about 15 carbon atoms, are preferred. Examples ofsuitable diisocyanates are trimethylene diisocyanate, tetramethylenediisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate,propylene diisocyanate, ethylethylene diisocyanate, 2,3-dimethylethylenediisocyanate, 1-methyltrimethylene diisocyanate, 1,3-cyclopentylenediisocyanate, 1,4-cyclohexylene diisocyanate, 1,2-cyclohexylenediisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate,2,4-toluylene diisocyanate, 2,6-toluylene diisocyanate, 4,4'-diphenylenediisocyanate, 1,5-naphthylene diisocyanate, 1,4-naphthylenediisocyanate,1-isocyanatomethyl-5-isocyanato-1,3,3-trimethylcyclohexane,bis(4-isocyanatocyclohexyl)methane, bis(4-isocyanatophenyl)methane,4,4'-diisocyanatodiphenyl ether and2,3-bis(8-isocyanatooctyl)-4-octyl-5-hexylcyclohexane. Polyisocyanatesof higher isocyanate functionalty can also be used. Examples of theseare tris(4-isocyanatophenyl)methane, 1,3,5-triisocyanatobenzene,2,4,6-triisocyanatotoluene, 1,3,5-tris(6-isocyanatohexyl)biuret,bis(2,5-diisocyanato-4-methylphenyl)methane, and polymericpolyisocyanates, such as dimers and trimers of diisocyanatotoluene. Inaddition, mixtures of polyisocyanates can also be used. Organicpolyisocyanates suitable as crosslinking agents in the invention canalso be prepolymers derived, for example, from a polyol, including apolyether polyol or a polyester polyol.

Any suitable aliphatic, cycloaliphatic or aromatic alkyl monoalcoholscan be used for the blocking of the polyisocyanates. Examples of theseare aliphatic alcohols, such as methyl, ethyl, chloroethyl, propyl,butyl, amyl, hexyl, heptyl, octyl, nonyl, 3,3,5-trimethylhexyl, decyland lauryl alcohols; cycloaliphatic alcohols such as cyclopentanol andcyclohexanol; aromatic alkyl alcohols, such as phenylcarbinol andmethylphenylcarbinol.

Other suitable blocking agents are hydroxylamines such as ethanolamine,oximes such as methyl ethyl ketone oxime, acetone oxime andcyclohexanone oxime, or amines such as dibutylamine anddiisopropylamine.

The polyisocyanates and blocking agents mentioned can also be used, insuitable proportions, for the preparation of the partially blockedpolyisocyanates described above.

The usual additives, such as, for example, coalescing solvents,pigments, surfactants, crosslinking catalysts, antioxidants, fillers andantifoams, can be added to the aqueous coating compositions preparedusing the binders according to the invention.

The aqueous systems prepared with the aid of the binders according tothe invention are especially suitable for the cationic electrocoatingprocess; they can, however, also be used in conventional coatingprocesses. Metals, for example, pretreated, if desired, such as iron,steel, copper, zinc, brass, magnesium, tin, nickel, chromium andaluminum, can be used as the coating substrate, and also impregnatedpaper and other electrically conducting substrates.

The binders according to the invention are also suitable for thepreparation of pigment pastes, ie. the binders can also be used asgrinding resins.

When the resin according to the invention is used as grinding resin forthe preparation of a pigment paste, the proportions of theepoxide-containing organic material and the organic tertiary amine whichare reacted with one another are preferably chosen such that the carrierresin contains 0.8 to 2.0 nitrogen atoms per molecule. Lower amounts ofquaternary nitrogen can lead to poor pigment wettability, while higheramounts result in the resins being too water-soluble.

Pigment pastes according to the invention are prepared by comminuting ordispersing a pigment in the grinding resin in well-known manner. Thepigment paste contains the grinding resin and at least one pigment asthe essential ingredients.

In addition, however, other usual additives can be present in thepigment composition, such as plasticizers, wetting agents, surfactantsor antifoams.

The grinding of the pigments usually takes place in ball mills,sandmills, Cowles mills and continuous mills, until the pigment has beencomminuted to the desired particle size and preferably is wetted by theresin or dispersed in it. After the comminution, the particle size ofthe pigment should be in the region of 10 microns or less. In general,comminution is carried out to a Hegman number of from about 6 to 8. Thegrinding is preferably carried out in an aqueous dispersion of thegrinding resin. The amount of water present in the composition to beground should be sufficient to form a continuous aqueous phase.

The well-known pigments can be used as pigments in the invention.Titanium dioxide is in general the sole or the principal white pigment.However, other white pigments or extenders, such as antimony oxide, zincoxide, basic lead carbonate, basic lead sulfate, barium carbonate,porcelain, clay, calcium carbonate, aluminum silicate, silica, magnesiumcarbonate and magnesium silicate can also be used. Examples of coloredpigments which can be used, are cadmium yellow, cadmium red, carbonblack, phthalocyanine blue, chromium yellow, toluidine red and hydratediron oxide. For further general hints on comminution of pigments andformulation of coating compositions, the following books should bereferred to; D. H. Parker, Principles of Surface Coating Technology,Interscience Publishers, New York (1965) R. L. Yates, Elektropainting,Robert Draper Ltd., Teddington England (1966) H. F. Payne, OrganicCoating Technology, Volume 2, Wiley and Sons, New York (1961).

The modified epoxy resins should be capable of preparation on anindustrial scale with as few problems as possible.

The invention also relates to a process for the preparation ofwater-dilutable binders for cationic electrocoating finishes based onmodified epoxy resins, containing ammonium, sulfonium and/or phosphoniumgroups.

In the synthesis as well as the modification of epoxy resins, epoxidegroups are opened with the formation of secondary hydroxyl groups. Thesecondary OH groups formed in this way can in turn undergo an additionreaction with an epoxide group, forming an ether bond and a newsecondary hydroxyl group.

In the industrial production of modified epoxy resins, difficulties mayarise due to a failure to control the reaction by a suitable choice ofreaction conditions to ensure that a sufficient number of reactiveepoxide groups are available for carrying out the desired modificationreactions and that no resins with excessively high viscosity and nounusable gels are obtained as reaction products.

Attempts have previously been made to avoid the production difficultiesoutlined above by very substantially suppressing the reaction betweensecondary hydroxyl groups and epoxide groups.

Thus, for example, it has been proposed to minimize the tendency to gelformation during the preparation of modified epoxy resins by achain-lengthening using organic polyols carrying at least two primaryalcoholic OH groups (U.S. Pat. No. 4,104,147) or polymercapto compounds(U.S. Pat. No. 4,260,720). The objective was to suppress reactionsbetween the secondary hydroxyl groups and the epoxide groups byreactions of the alcoholic primary OH groups more reactive towardepoxide groups, or mercapto groups, with the epoxide groups.

However, this method of controlling the reaction has the disadvantagethat at least 2 new secondary hydroxyl groups are formed in eachchain-lengthening step.

A further object of the present invention was to find better ways forsolving the production difficulties described above.

Surprisingly, this object was achieved by preparing the modified epoxyresins by a process in which a di-epoxide compound and/or a mixture ofdi-epoxide compounds, together with at least one mono-epoxide compoundif desired, are converted to an epoxy resin in which the di-epoxidecompound and the initiator are incorporated in a molar ratio of >2:1 to10:1, by a polyaddition reaction initiated by a monofunctionallyreacting initiator carrying either an alcoholic OH group, a phenolic OHgroup or an SH group, and carried out at 100° to 195° C., if desired inthe presence of a catalyst; and by subsequently modifying the epoxyresin obtained in this manner by a reaction with

(A) primary and/or secondary amines or their salts and/or the salt of atertiary amines a sulfide/acid mixture or phosphine/acid mixture or amixture of these compounds, and, if desired, with

(B) a polyfunctional alcohol, a polycarboxylic acid, a polyamine, apolysulfide, a polyphenol or a mixture of these compounds

and in which the water-dilutability is obtained, if desired, byprotonization with a water-soluble acid.

As demonstrated by the reaction scheme given below, the epoxy resinmolecules, formed by a polyaddition reaction initiated by amonofunctionally reacting initiator, contain one single secondaryhydroxyl group.

In the process according to the invention, the number of the secondaryhydroxyl groups formed can be controlled in a simple manner in such away that the production difficulties mentioned above do not occur andthe reaction between secondary hydroxyl groups and epoxide groupsoccurring as undesirable side reaction can now be utilized as apurpose-controlled main reaction for resin synthesis.

The reaction scheme of the synthesis of the epoxy resin by apolyaddition reaction of di-epoxide compounds (for example bisphenol Adiglycidyl ether) initiated by a monofunctionally reacting initiator(for example R-OH):

1. Initiation reaction:

The initiator reacts with an epoxide group with the formation of asecondary hydroxyl group: ##STR4##

2. Reaction steps for synthesizing the resin: ##STR5##

The process according to the invention is carried out in the followingway:

The monofunctionally reactive initiator and the di-epoxide ormono-epoxide compounds are mixed in a molar ratio of 1:1 and allowed toreact fully at temperatures between 100° and 195° C., preferably 115°and 185° C., in the presence or absence of a catalyst. (The completionof the reaction can be checked by determination of the epoxideequivalent weight.) Thereafter further di-epoxide or mono-epoxidecompounds can be added under the same reaction conditions.

The polyaddition can also be carried out by allowing the total amount ofthe epoxide compounds to be used to react with the initiator in onestep.

In both cases the reaction is arranged so that the polyaddition productincorporates the di-epoxide compound and the initiator in a molar ratioof >2:1 to 10:1.

This reaction product can then be modified with the component A andalso, if desired, with the component B. The reaction with the componentB can also take place before the reaction with the component A.

The reaction between amines and epoxide group-containing compounds oftensets in as early as when the reactants are mixed. Depending of thecourse of reaction desired, it is recommended to raise the reactiontemperature to 50° to 150° C., mainly to allow the reaction to go tocompletion.

The amount of amine used for the reaction with the epoxide-containingcompound should be at least such that the resin acquires a cationiccharacter, ie. that it migrates to the cathode in the coating bath underthe influence of a voltage, when it has been made soluble by theaddition of an acid. Essentially, all epoxide groups of the resin can bereacted with an amine. However, it is also possible to leave an excessof epoxide groups in the resin.

A further possibility of achieving the required water dispersabilityconsists of using Mannich bases, ie. reaction products of suitablephenols carrying groups capable of reacting with an epoxide ring, withformaldehyde and a secondary amine. In this way the binder becomes atthe same time self-crosslinking.

The reaction with amine acid salts takes place at temperatures from 20°to 110° C. The reaction can take place without the addition of solvents,but in the presence of solvents, such as aromatic hydrocarbons ormonoalkyl ethers of ethylene glycol, it becomes more easilycontrollable.

The ratio between the amine acid salt and the epoxide compound canfluctuate and the optimum ratios depend on the specific startingmaterials. In general, about 1 to about 50 parts by weight of salt areused for 100 parts by weight of polyepoxide. In general, the ratio ischosen according to the content of nitrogen derived from thequaternizing agent, which typically is about 0.05 to about 16%, based onthe total weight of the amine salt and the polyepoxide.

The sulfide/acid mixture and the epoxide compound are reacted by mixingthe components and warming them, usually to moderately elevatedtemperatures, such as from 70° to 110° C. A solvent is unnecessary,although one is frequently used to control the reaction better. Suitablesolvents are aromatic hydrocarbons, monoalkyl ethers or ethylene glycoland aliphatic alcohols. The proportions of the sulfide and the epoxidecompound can vary, and the optimum ratios of the two components dependon the specific starting materials. However, about 1 to 50 parts byweight of sulfide are usually used per 100 parts by weight of theepoxide compound. The proportions are frequently based on the sulfurcontent, which typically is from about 0.1 to 35%, based on the totalweight of the sulfide and the epoxide compound.

The phosphine/acid mixture and the epoxide compound are reacted bymixing the components, occasionally warming the reaction mixture tomoderately elevated temperatures. The reaction temperature is notparticularly critical and depends on the starting materials and theirreaction velocities. The reaction is frequently satisfactorily rapid atroom temperature or at temperatures raised to up to 70°. In some casesit is advisable to use higher temperatures, such as about 110° C. orhigher. A solvent is unnecessary, although one can frequently be used tocontrol the reaction better. Examples of suitable solvents are aromatichydrocarbons, monoalkyl ethers of ethylene glycol and aliphaticalcohols. The proportions of the phosphine and the epoxide compound canbe varied and the optimum proportions depend on the specific startingmaterials. Normally, however, from about 1 to about 50 parts by weightof phosphine are used per 100 parts by weight of the epoxide compound.The proportions are frequently given with reference to the proportion ofphosphine, about 0.1 up to about 35% by weight of phosphine, based onthe total weight of phosphine and epoxide compound, being typicallyused.

The modification with the component B is carried out at reactiontemperatures of 80° to 170° C. The course of the reaction of thepolyaddition product with the components A and, if desired, B, can befollowed by the respective determination of the epoxide equivalentweight.

The invention also relates to a process for the electrophoretic coatingof an electrically conducting substrate connected as a cathode, in anaqueous bath which contains, besides the usual additives,water-dilutable cationic binders which have been either madeself-cross-linkable by reaction or can be crosslinked by crosslinkingagents present in the bath, wherein the binders are prepared by

(a) a polyaddition of a di-epoxide compound and/or a mixture ofdi-epoxide compounds, together with at least one mono-epoxide compoundif desired, carried out at 100° to 195° C., if desired in the presenceof a catalyst, and initiated by a monofunctionally reacting initiatorcarrying either an alcoholic OH group, a phenolic OH group or an SHgroup, to form an epoxy resin in which the di-epoxide compound and theinitiator are incorporated in a molar ratio of >2:1 to 10:1, and by asubsequent

(b) modification of the epoxy resin obtained from (a) with

(A) a primary and/or secondary amine or their salts and/or a salt oftertiary amine, a sulfide/acid mixture or phosphine/acid mixture or amixture of these compounds, as well as, if desired, with

(B) a polyfunctional alcohol, a polycarboxylic acid, a polyamine, apolysulfide, a polyphenol or a mixture of these compounds, and, ifdesired,

(c) by protonization with a water-soluble acid.

For the cationic deposition, the objects to be coated are immersed in anaqueous dispersion of the solubilized film-forming cationic binder. Anelectric voltage is applied between the object to be coated, whichserves as the cathode, and an anode, and the cationic binder isdeposited on the cathode with the aid of the electric current. Theobject is then removed from the bath and usually rinsed. The coating isthen cured by warming in the usual manner.

Advantageous embodiments of the process according to the invention areoutlined in claims 9 to 15.

The invention is further clarified by the examples below. All parts andpercentages are by weight, unless expressly stated otherwise.

Preparation of a crosslinking agent I

A blocked isocyanate crosslinking agent (polyurethane crosslinkingagent) is prepared according to German Offenlegungsschrift 2,701,002,Example 1, by adding, slowly and with stirring in a nitrogen atmosphere,218 parts of 2-ethylhexanol to 291 parts of an 80/20 isomeric mixture of2,4-/2,6-toluylene diisocyanate, the reaction temperature beingmaintained below 38° C. by external cooling. The reaction mixture ismaintained at 38° C. for a further half hour and is then warmed to 60°C., after which 75 parts of trimethylolpropane are added, followed by0.08 parts of dibutyltin dilaurate as catalyst. After an initialexothermic reaction the mixture is kept 1.5 hours at 121° C., untilessentially all the isocyanate groups are used up, which is recognizedfrom the infrared spectrum. The mixture is then diluted with 249 partsof ethylene glycol monoethyl ether.

Preparation of crosslinking agent II

A crosslinking agent which possesses β-alkoxyalkyl ester groups whichare active in the crosslinking is prepared as follows:

1462 g of hexyl glycol (10 mol) are placed in a reaction vessel providedwith a water separator, reflux condenser and interconnected Raschigcolumn and heatable by heat-transfer oil, and 1000 g of succinicanhydride (10 mol) are added while passing in an inert gas and stirring.The reaction mixture is heated to 120° C., the exothermic heat ofreaction briefly raising the temperature to 130° C. The temperature ismaintained until the acid number reaches 230 mg of KOH/g.

400 g of xylene, 5 g of N-cetyl-N,N,N-trimethylammonium bromide and 940g of a bisphenol A-epoxide resin with an epoxide equivalent weight of188 (2.5 mol) are then added. The temperature is again raised to 130° C.in the course of one hour and maintained at this temperature until theepoxide value has dropped to zero. After an addition of 2 g ofparatoluenesulfonic acid solution (25% in n-propanol), the temperatureis raised to 200° C. in the course of 4 hours, during which time thereaction water formed is continuously removed. After a furthertemperature rise to 220° C., the temperature is maintained until about90 g of water have separated off and the acid number has dropped tobelow 2 mg of KOH/g of solid resin. The reaction mixture is then cooledand discharged without dilution.

Solids: 95.2% by weight (measured by heating for 1 hour at 130° C.).

Acid number: 1.1 mg of KOH/g of solid resin.

Viscosity: 480 mPas (measured after dilution with methyl isobutyl ketoneto 70% by weight at 25° C.).

Preparation of a crosslinking agent III

2340 g of the glycidyl ester of 2-methyl-2-ethylheptanoic acid areheated in a reaction vessel with 2073 g of trimellitic acid anhydride to130° C. A strongly exothermic reaction begins. The reaction ismaintained at 150° C. by external cooling, until an acid number of 183is reached. The reaction mixture is then cooled to 90° C. and 1450 g ofmethyl isobutyl ketone (MIBK) are added. Subsequently 835 g of propyleneoxide are slowly added dropwise. The reaction is interrupted when anacid number of 2 is reached. The solids content of the resin solution isadjusted to 70% by adding further MIBK.

Preparation of a binder I

1805 parts of a liquid epoxy resin based on bisphenol A with an epoxideequivalent weight of 188 are placed in a reaction vessel provided with astirrer, reflux condenser, internal thermometer and a nitrogen inlet,together with 450 parts of nonylphenol, 63 parts of xylene and 7 partsof dimethylbenzylamine. The reaction mixture is heated to 130° C. andmaintained at this temperature until the epoxide equivalent weightreaches a value of 460. 440 parts of xylene are then added and themixture is cooled to 80° C. A mixture of 126 parts of diethanolamine and90 parts of N-methylethanolamine is added dropwise. The reaction isallowed to proceed at this temperature for 1 hour, after which 73 partsof ethanolamine are added dropwise, the reaction mixture is maintainedfor a further 2 hours at this temperature and subsequently diluted with127 parts of hexyl glycol. A clear resin solution with a solids contentof 80% and a MEQ base value of 1.45 milliequivalents/g of solid resin isobtained.

Preparation of a binder II

The procedure for the preparation of the binder I is followed. Theepoxide equivalent weight (EEW) approaches 400 in this case. Themodified weights used are as follows:

    ______________________________________                                        Epoxy resin (EEW = 188)                                                                             2,000                                                   tert-Butylphenol      139                                                     Xylene                 60                                                     Dimethylbenzylamine    8                                                      Xylene                406                                                     Diethanolamine        280                                                     N,N--dimethylaminopropylamine                                                                       136                                                     Hexyl glycol          166                                                     n-propanol            413                                                     ______________________________________                                    

A clear resin solution with a solids content of 74.8% (measured for 1hour at 190° C.) and a MEQ base value of 2.15 milliequivalents/g ofsolid resin is obtained.

Preparation of a binder III

In a similar manner to the preparation of the binder I, 1805 parts of anepoxy resin (EEW=188), 352 parts of nonylphenol, 67 parts of xylene and10 parts of dimethyllaurylamine are allowed to react at 130° C. until anepoxide equivalent weight of 450 is reached. A 71.3% solution ofethanolamine/methyl isobutyl ketimine in methyl isobutyl ketone is addeddropwise in the course of 1 hour at this temperature. The reaction isallowed to proceed for a further 7 hours, and the mixture is thendiluted to a solids content of 83.5% (1 hour at 130° C.) with 141 partsof hexyl glycol. The resin has a MEQ base value of 1.68milliequivalents/g of solid resin.

Preparation of aqueous dispersions I-IV

The binders are then converted to aqueous dispersions by mixing thecomponents listed in the table below and adding deionized water (case1). After 20 minutes' homogenization, the mixture is further diluted,batchwise, with deionized water (case 2). The dispersions aresubsequently subjected to a brief vacuum distillation, the organic phasebeing separated off from the distillate.

    ______________________________________                                        Dispersions   I        II      III    IV                                      ______________________________________                                        Binder I      937      937     --     --                                      Binder II     --       --      1002   --                                      Binder III    --       --      --     898                                     Crosslinking agent I                                                                        --       528     --     528                                     Crosslinking agent III                                                                      --       --      388    --                                      Crosslinking agent IV                                                                       528                     --                                      Dibutyltin dilaurate                                                                        --       8       --     8                                       Solution of lead(II)                                                                        28       --      28     --                                      octoate (24% Pb)                                                              Antifoam solution                                                                           1.2      1.2     1.2    1.2                                     Glacial acetic acid                                                                         26.1     26.1    29.1   33.7                                    Deionized water 1                                                                           748      748     820    780                                     Deionized water 2                                                                           1493     960     2240   1760                                    Solids        31.8%    35.1%   26.4%  28.5%                                   (1 hour at 130° C.)                                                    ______________________________________                                    

Preparation of a gray pigment paste

800 parts of butyl glycol are added to 953 parts of a commercial epoxyresin based on bisphenol A with an epoxide equivalent weight of 890. Themixture is heated to 80° C. 221 parts of a reaction product from 101parts of diethanolamine and 120 parts of an 80% aqueous lactic acid arethen added to the resin solution. The reaction is carried out at 80° C.until the acid number has dropped below 1.

1800 parts of this product are initially taken with 2447 parts ofdeionized water, followed by addition of 2460 parts of TiO₂, 590 partsof an extender based on aluminum silicate, 135 parts of lead silicateand 37 parts of carbon black. This mixture is comminuted by grinding toa Hegman number of 5 to 7. 1255 parts of deionized water are added inorder to obtain the desired paste consistency. This gray paste has avery long shelf life.

Preparation of electrocoating baths I to IV

The binder dispersion is mixed with the gray pigment paste in thefollowing ratio

    ______________________________________                                        Bath              Binder  Paste                                               ______________________________________                                        I           I         2201    775                                             II          II        2000    775                                             III         III       2651    775                                             IV          IV        2456    775                                             ______________________________________                                    

The bath solids are adjusted to 20% with deionized water (150° C., 30minutes). The bath is then allowed to age for 3 days, with stirring. Thedeposition of the paint films on zinc phosphated panels takes place inthe course of 2 minutes. The bath temperature is 27° C. The depositedfilms are baked at 180° C. for 20 minutes.

    ______________________________________                                        Results of depositions                                                                   Bath I                                                                              Bath II  Bath III Bath IV                                    ______________________________________                                        Deposition voltage                                                                         250 V   310 V    300 V  270 V                                    Film thickness                                                                             28 μm                                                                              26 μm 20 μm                                                                             29 μm                                 MIBK test*   satis-  satis-   satis- satis-                                                factory factory  factory                                                                              factory                                  Course**     1.5     1        1      1.5                                      Crosshatch** 0       0        0      0                                        Erichsen indentation                                                                       7.8 mm  9.2 mm   8.7 mm 8.3 mm                                   ______________________________________                                         *20 double rubs with a cottonwool wad soaked in MIBK                          **0 = best, 5 = worst                                                    

We claim:
 1. A water-dilutable binder for cationic electrocoatingfinishes, comprising:a reaction product of an epoxy resin and an amine,sulfide or phosphine compound; wherein the epoxy resin comprises apolyepoxide-polyether, synthesized from a diepoxide compound and amonofunctionally reacting initiator carrying an alcoholic OH group, aphenolic OH group or an SH group, the diepoxide compound or compoundsand the initiator being incorporated in a molar ratio of greater thanabout 2:1 to about 10:1, and the synthesis being conducted underreaction conditions sufficient to produce a polymer having a polyetherbackbone with pendant unreacted epoxy groups; and, the amine, sulfide orphosphine compound comprises a primary amine, a secondary amine, amixture thereof or a salt thereof, a salt of a tertiary amine, asulfide/acid mixture, a phosphine/acid mixture or a mixture of any ofsaid amines, sulfide/acids or phosphine/acids.
 2. A binder according toclaim 1 wherein the initiator is an alcohol of the formula R¹ OH whereinR¹ is alkyl of 1 to 20 carbons; alkenyl of 1 to 6 carbons; cycloalkyl;alkylphenol having 1 to 20 carbons in the alkyl group; alkoxyphenylhaving 1 to 10 carbons in the alkoxy group; aryl; aralkyl; R² --X--R³--, R² being alkyl of 1 to 6 carbons or phenyl, R³ being --CH₂ CH₂--(O--CH₂ CH₂)_(n) --, n being 0 or an integer of 1 to 10, X being O orS; or,the initiator is a mercaptan of the formula R⁶ SH wherein R⁶ isalkyl of 1 to 20 carbons; cycloalkyl; aryl; aralkyl; or R⁷ O₂C(CH₂)_(n), R⁷ being alkyl of 1 to 8 carbons.
 3. A binder resinaccording to claim 1 wherein the epoxy resin comprises aself-polyaddition product of the initiator and a mixture of a diepoxidecompound or compounds and a monoepoxide compound.
 4. A binder accordingto claim 3 wherein the diepoxide and monoepoxide compounds have epoxideequivalent weights of below about
 500. 5. A binder according to claim 1wherein the diepoxide compound or compounds have epoxide equivalentweights below about
 500. 6. A binder according to claim 5 wherein thediepoxide compound is a Bisphenol A diglycidyl ether.
 7. A binderaccording to claim 1 wherein the epoxy resin is reacted with an extendercomponent selected from the group consisting of a polyhydric alcohol, apolycarboxylic acid, a polyamine, a polysulfide, a polyphenol ormixtures thereof, to form an extended epoxy resin which is reacted withthe amine, sulfide or phosphine compound to form the binder resin.
 8. Abinder according to claim 7 wherein the extender component has amolecular weight of from about 100 to about
 3500. 9. A binder accordingto claim 7 wherein the proportion of extender component present is fromabout 5 to 60 percent by weight relative to combined weight of theself-polyaddition product and the extender component, the molar ratio ofthe self-polyaddition product to extender component being from 4:1 to0.8:1.
 10. A binder according to claim 9 wherein the molar ratio isabout 2:1.
 11. A binder according to claim 7 wherein the extendercomponent is a polyphenol or a mixture of polyphenols of formula I:##STR6## wherein X is alkylene, arylene, alkarylene; --O--,--O--alkylene, --O-arylene, --O-alkarylene; --S--, --S-alkylene,--S-arylene, --S-alkarylene; --CO--, --CO-alkylene, --CO-arylene,--CO-alkarylene; --NH--, --NH-alkylene, --NH-arylene or--NH-alkarylene;n is 0 or 1; Y is X, ##STR7## Z is a polyester,polyether, polyamide, polycarbonate or polyurethane radical; and R is H,CH₃, alkyl, --CH₃, --O-alkyl, --NO₂, --NR'R", --NHCOR", R' and R" eachbeing H, alkyl, aryl or aralkyl; provided that when Y is X, X is otherthan O, S or NH and that when Y is CO, X is other than CO.
 12. Acrosslinkable binder composition comprising a binder of claim 1 incombination with a crosslinking agent or a binder of claim 1 renderedself-crosslinkable by reaction with a crosslinking agent.
 13. A processfor the preparation of a water-dilutable binder for cationicelectrocoating finishes, comprising:reacting a diepoxide compound orcompounds with a monofunctionally reacting initiator having an alcoholicOH group, a phenolic OH group, or an SH group to form an epoxy resin,the molar ratio of the diepoxide compound or compounds and the initiatorbeing from about 2:1 to about 10:1 and the reaction conditions producinga polyepoxide-polyether having a polyether backbone with pendantunreacted epoxy groups; and then reacting the epoxy resin with an amine,sulfide or phosphine compound selected from the group consisting of aprimary amine, a secondary amine, a mixture thereof or a salt thereof, asalt of a tertiary amine, a sulfide/acid mixture, a phosphine/acidmixture or a mixture of any of the amines, sulfide/acids orphosphine/acids to produce the binder.
 14. A process according to claim13 comprising self-polyadding a mixture of the diepoxide compound orcompounds and at least one monoepoxide compound.
 15. A process accordingto claim 14 wherein the diepoxide and monoepoxide compounds have epoxideequivalent weights below
 500. 16. A process according to claim 13wherein the diepoxide compound or compounds have epoxide equivalentweights below
 500. 17. A process according to claim 16 wherein thediepoxide compound is a Bisphenol A diglycidyl ether.
 18. A processaccording to claim 30 wherein the self-polyadding step includes acatalyst.
 19. A process according to claim 13 further comprisingreacting the epoxy resin with an extender component selected from thegroup consisting of a polyhydric alcohol, a polycarboxylic acid, apolyamine, a polysulfide, a polyphenol and mixtures thereof, to form anextended epoxy resin which is then reacted with the amine, sulfide orphosphine compound to form the binder resin.
 20. A process according toclaim 19 wherein the extender component has a molecular weight of fromabout 100 to
 3500. 21. A process according to claim 19 wherein theextender component is a polyphenol or a mixture of polyphenols offormula I: ##STR8## wherein X is alkylene, arylene, alkarylene; --O--,--O-alkylene, --O-arylene, --O-alkarylene; --S--, --S-alkylene,--S-arylene, --S-alkarylene; --CO--, --CO-alkylene, --CO-arylene,--CO-alkarylene; --NH--, --NH-alkylene, --NH-arylene or--NH-alkarylene;n is 0 or 1; Y is X, ##STR9## Z is a polyester,polyether, polyamide, polycarbonate or polyurethane radical; and R is H,CH₃, alkyl, --CH₃, --O-alkyl, --NO₂, --NR'R", --NHCOR", R' and R" eachbeing H, alkyl, aryl or aralkyl; provided that when Y is X, X is otherthan O, S or NH and that when Y is CO, X is other than CO.
 22. A binderaccording to claim 1 wherein the hydroxyl functionality of the epoxyresin is substantially the same as or higher than that of the diepoxidecompound from which it was synthesized.
 23. A process according to claim13 wherein the hydroxyl functionality of the epoxy resin issubstantially the same as or higher than that of the diepoxide compoundfrom which it was synthesized.